Trust enhancement by multiple random beacons

TL;DR

The paper proposes a method to enhance trustworthiness of random beacons by combining multiple sources through XOR, ensuring unpredictability if at least one beacon is honest, and discusses limitations of hash-based methods.

Contribution

It introduces a strategy to improve beacon trustworthiness by combining multiple beacons, including spacelike-separated and time-sharing approaches, and analyzes their security advantages.

Findings

XORing multiple beacons increases trustworthiness if at least one is honest.

Spacelike separation enhances security against dishonest beacons.

Hash-based methods have notable disadvantages compared to XOR combination.

Abstract

Random beacons-information sources that broadcast a stream of random digits unknown by anyone beforehand-are useful for various cryptographic purposes. But such beacons can be easily and undetectably sabotaged, so that their output is known beforehand by a dishonest party, who can use this information to defeat the cryptographic protocols supposedly protected by the beacon. We explore a strategy to reduce this hazard by combining the outputs from several noninteracting (eg spacelike-separated) beacons by XORing them together to produce a single digit stream which is more trustworthy than any individual beacon, being random and unpredictable if at least one of the contributing beacons is honest. If the contributing beacons are not spacelike separated, so that a dishonest beacon can overhear and adapt to earlier outputs of other beacons, the beacons' trustworthiness can still be enhanced to a lesser extent by a time sharing strategy. We point out some disadvantages of alternative trust amplification methods based on one-way hash functions.